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*Two horses on either side of a canal pull a canal boat of mass 1.0*10^4 kg at a constant speed for a distance of 10.0 km. (Figure 7.32). One horse exerts a force of 3.0*10^2 N at an angle of 20º to the canal, and the other exerts 5.0 * 102 N. Find the work done by each horse and the work done by friction between the boat and the water.*

I believe I would set it up like this:

Call the direction parallel to the canal the x axis

The work of a horse whose angle is given will be the x-component of the force * distance in meters

[tex]W_{horse1}=cos(20)*3*10^2N*10000m[/tex]

The work done by the horse whose angle is not given will be the same as the first horse. Again, it will be the x-component of the force, which will be equal to Horse 1's x-component, and although the question doesn't ask for it, I could now compute Horse 2's angle.

But the work done by the friction between the boat and the water? I don't know how to solve that? What if the question said they were on ice instead of water?

The best I can come up with is

[tex]W_{friction}=Force_{friction} * 10000 meters[/tex]